The Audio Engineering Society (AES) has developed a standard for the serial transmission of two channels of audio data over shielded twisted-pair conductors, as embodied in AES Standard AES3-1992 titled “AES Recommended Practice for Digital Audio Engineering—Serial Transmission Format for Two-Channel Linearly Represented Digital Audio Data”, which is incorporated herein by reference.
The AES standard for two-channel serial transmission is designed to accommodate a signal having audio sub-frames of a fixed transport length. The standard accommodates either 24-bit audio sub-frames, or 20-bit audio sub-frames with an additional four-bit auxiliary data field. This results in an inefficient use of bandwidth when used with signals having different resolutions. Moreover, the audio compression standard is adapted to transmit only a limited amount of data relating to the audio stream. There is a need for a system which can accommodate different transport lengths within a single audio stream, and which allows for the ability to embed other data.
Data compression is commonly used in the transmission of digital audio signals in broadcasting and network communications. The compression of audio data increases the rate at which data can be transmitted in a serial format. A compression technique, called apt-X, has been developed which can be employed to compress audio signals in 16-bit, 20-bit, or 24-bit resolution AES format by a factor of 4 to 1. The apt-X compressed audio can then be formatted to be carried on AES equipment. However, previous implementations of apt-X compression required the number and resolution of the signals input to the compression system to be determined in advance, and did not allow the number and resolution of the signals carried to be easily changed, nor did it allow the transportation of additional data.